Hydroxyurea is a chemotherapeutic agent which has been successful in increasing fetal hemoglobin production in a small number of patients with Sickle Cell Disease. Here we propose to join a cooperative study to determine the optimum dose, schedule, and short-term toxicities in severely affected adults with Sickle Cell Disease. We have previous experience with this agent given in pulses in high doses, in this study. We will use continuous low- dose therapy to optimize the efficacy and patient acceptability, and minimize toxicity. We anticipate enrolling three patients.